Please help i will mark brainliest

Can someone me with questions 15 to 17 plz.

What is the empirical formula of c6h18o3? ch3o c2h5o c2h6o c2h5o5

Need what is special about water as a compound? how does water regulate climate? what drives water evaporation?   why is the water vapor fresh water when it rises from the ocean? why might freshwater in the form of snow take longer to enter the water cycle again than liquid precipitation?   what is an aquifer? what role do people play in the water cycle? plz just answer as many as you can ! thx if you !